What are the side effects of ivermectin?

Ivermectin Side Effects

Ivermectin commonly causes mild side effects including dizziness, nausea, headache, and rash, but can cause serious neurological toxicity in certain populations, particularly when used in inappropriate doses or formulations. 1

Common Side Effects

• Mild and short-duration effects 1, 2:
  • Dizziness
  • Nausea and vomiting
  • Headache
  • Rash and pruritus (itching)
  • Abdominal pain
  • Diarrhea
  • Fatigue/asthenia

Serious Adverse Effects

Neurological Toxicity

• Encephalopathy: Particularly in patients with Loa loa infection 1
• Severe neurological symptoms with overdose or veterinary formulations 3, 4:
  • Altered mental status
  • Seizures
  • Ataxia (loss of coordination)
  • Visual hallucinations
  • Confusion

Hepatic Effects

• Elevated liver enzymes 5
• Potential hepatitis with abdominal pain and nausea 6

Cardiovascular Effects

• Sinus tachycardia (reported in elderly patients) 6
• Hypotension with significant overdose 1

Risk Factors for Adverse Effects

Patient-Specific Factors

• Loa loa infection: Patients with exposure to Loa loa-endemic areas of West or Central Africa are at risk for potentially fatal encephalopathy 1
• Onchocerciasis: Patients with hyperreactive onchodermatitis (sowda) may experience severe reactions including edema 1
• Elderly patients: Higher risk of adverse effects, particularly cardiac dysfunction and liver disease 6
• P-glycoprotein genetic polymorphisms: May increase neurological toxicity 2

Medication-Related Factors

• Veterinary formulations: Associated with higher doses and more severe toxicity 3, 4
• Self-medication: Particularly dangerous when using non-human formulations 3
• Drug interactions:
  • Increased INR when co-administered with warfarin 1
  • P-glycoprotein inhibitors may increase toxicity 2
  • Azithromycin can significantly increase serum ivermectin concentration 5

Special Populations

Pregnancy

• Teratogenic in animal studies: Cleft palate and clubbed forepaws observed 1
• Not recommended during pregnancy: Safety in pregnancy has not been established 1
• If required during pregnancy: Consider avoiding first trimester 5

Breastfeeding

• Low concentration excreted in breast milk: Likely compatible with breastfeeding 5, 7
• Treatment of breastfeeding mothers should only be undertaken when benefits outweigh risks 1

Children

• Safety not established in children weighing less than 15 kg 1

Proper Administration to Minimize Side Effects

• Take with food: High-fat food increases bioavailability by 2.5 times 5
• Avoid alcohol: Reported to worsen side effects 5
• Proper dosing: Most toxicity occurs with supratherapeutic doses 3, 4
• Exclude Loa loa infection: Before treating patients with travel history to endemic regions 7, 1

Management of Overdose or Toxicity

• Supportive care:
  • Parenteral fluids and electrolytes
  • Respiratory support if needed
  • Pressor agents for significant hypotension
• Decontamination:
  • Activated charcoal may be beneficial 8
  • Gastric lavage for recent ingestions 1

Key Monitoring Considerations

• Liver function: Monitor for hepatotoxicity 5, 6
• Neurological status: Particularly in high-risk patients 1
• ECG monitoring: Recommended before treatment in some cases 5

Ivermectin should only be used for approved indications, as inappropriate use (such as for COVID-19) is associated with unnecessary risk of adverse effects without proven benefit 5, 2.